Many new drugs, including proteins, peptides and DNA constituents, have been developed for better and more efficient treatment for disease and illness. Especially due to recent advances in molecular biology and biotechnology, increasingly potent pharmaceutical agents, such as recombinant human insulin, growth hormone and erythropoeitin are available. However, a major limitation in using these new drugs is lack of an efficient drug delivery system; a drug must be transported across one or more biological barriers in the body at rates and in amounts that are therapeutically effective.
Most drugs are orally administered. However, some drugs, especially protein and peptide drugs, cannot be effectively adsorbed in this manner because of severe degradation in the gastrointestinal tract, poor absorption in intestinal membrane and/or first pass breakdown by the liver.
Another administration technique is parental injection, using standard syringes or catheters. Needle injection provokes needle phobia, substantial pain, local damage to the skin in many patients. Withdrawal of body fluids, such as blood, for diagnostic purposes provokes similar discomforts. Further, needle injection is not ideal for continuous delivery of a drug, or for continuous diagnosis.
Another drug delivery technique is transdermal delivery, which usually relies on diffusion of a drug across the skin. This method is not broadly applicable because of the poor skin permeability of many drugs. The outermost layer of skin, stratum corneum, represents a major barrier to transdermal drug penetration. Once a drug reaches the dermal depth (below the epidermal layer), the drug diffuses rapidly to deep tissue layers and other parts of the system via blood circulation.
In an attempt to improve the rate of drug delivery through the skin, chemical enhancers, iontophoresis, electroporation, ultrasound, and heat elements have been used to supplement drug delivery. However, these techniques are not suitable for some types of drugs and often fail to provide a therapeutic level of delivery. These techniques sometimes result in undesirable skin reactions and/or are impractical for continuous controlled drug delivery over a period of hours or days.
Other attempts, such as particle or liquid injection, have been made to design alternative techniques to transfer drugs transdermally. A main advantage of those techniques is absence of needle use and reduction of incidence of contamination. However, liquid injection frequently causes some pain and/or sub-dermal hemorrhage. One technique, ballistic particle injection, is hard to administer exactly and continuously and can cause micro-bleeding.
Other attempts, such as micro-needle drug delivery, have been developed using micro-fabrication procedures from the semiconductor industry. While the conventional devices have some uses, most of these devices are designed for drug delivery through a hollow interior of a needle or along an outer surface of a needle. However, because most of these needles are made from brittle silicon materials, needle breakage under the skin is a possibility. Some devices are used as skin perforators for subsequent patch drug application. There remains a need for better drug delivery devices that rely on smaller incisions, deliver drug with greater efficiency and less variability of drug administration, and/or are easier and safer for a patient to use.
What is needed is an approach that reduces or controls the skin barriers to permit controlled introduction of one, two or more drugs, simultaneously or sequentially, and to provide prompt initiation and cut-off of drug delivery with improved efficiency and safety.